Fuel injection valve for preliminary and main injection



Oct. 1, 1968 H. EIDTMANN ET AL 3,403,861

FUEL INJECTION VALVE FOR PRELIMINARY AND MAIN INJECTION Filed March 50, 1967 INVENTORS United States Patent O ,422 6 Claims. (Cl. 239-533) ABSTRACT OF THE DISCLOSURE A fuel injection valve assembly for supplying a preliminary injection of fuel of a constant amount regardless of engine speed before the main injection of fuel begins comprising a spring biased, fuel supply pressure responsive, preliminary injection piston for the preliminary injection, a fuel supply pressure responsive loading piston for controlling the main injection fuel flow and a needle valve, both of the latter being biased oppositely by a common spring. Separate supply ducts for the preliminary and main fuel injections and the arrangement of the valve surfaces on the loading piston and needle valve enable the loading piston to be held closed and the needle valve to be opened by the pressure imposed on the preliminary injection piston and remain open long enough for the preliminary injection piston to travel its full stroke before closing and before the needle valve is opened for the main injection.

Field of the invention The present invention relates to a fuel injection nozzle and more particularly to an injection valve for both preliminary fuel injection as well as main fuel injection and involves a construction in which the fuel injection valve needle opens under pressure of fuel being supplied to a chamber through which the valve needle extends and against the pressure of a spring loaded by a piston which is adapted to control the fuel supply duct for the main injection fuel flow. The fuel injection valve assembly further includes a spring biased preliminary injection piston which is also subjected to pressure of the incoming fuel and is so arranged that during the first phase of the supply operation it moves counter to the spring pressure and injects a charge of fuel into the aforementioned chamber. Substantially simultaneously with this charge being injected into the chamber the spring loaded piston is moved, because of the constant fuel supply, against an abutment thus increasing the force of the spring, and, finally with the further increase of pressure of the fuel being supplied, the valve needle for the main injection charge opens.

Description of the prior art In the prior art fuel injection valves of this type it is known that the loading piston controls and opens the supply channel for the main injection charge to the pressure chamber of the injection valve before the preliminary injection piston has completed its path of travel whereby the quantity of the preliminary injection is reduced. This is so because, in these valves, the preliminary injection piston, after having completed a specific path of its preliminary injection stroke, controls and opens a bore through which the fuel under pressure will then flow to the loading piston, which, in turn, will then control and open the supply channel for the main fuel injection charge to the pressure chamber of the injection valve. Since the main injection charge also flows through the bore which is controlled by the preliminary injection piston, the crosssection being opened by the preliminary injection piston 3,493,861 Patented Oct. 1, 1968 must be so large that this quantity of charge can flow therethrough also at high speed without major pressure loss. In addition thereto, it must be noted that in vehicle motors, for example, the preliminary injection charge is 5 to 10 mm. which, in a favorable construction, corresponds to a stroke of 1 to 2 mm. of the preliminary injection piston, It is apparent, therefore, that the preliminary injection piston must begin to open the aforementioned bore at the latest after having completed half the stroke thereof. At loW speed, however, there sufiices a smaller cross-section than would be necessary at high speed which is the reason why the preliminary injection piston is not displaced into contact with the stop and the preliminary injection charge thus becomes correspondingly smaller than it would be at high speed.

Another disadvantage, whose effects are noticeable particularly at low speed, is the relatively great amount of leakage at the slide or valve guides as a result of the small overlap of the slide or valve faces which is due to structural reasons. The preliminary injection charge is consequently further. reduced thereby. Also, the fuel flow with several deflections of about and sudden crosssectional changes which is unfavorable from the point of view of flow techniques and equally due to structural reasons, produces pressure losses and a temperature increase. The viscosity of the fuel which decreases with the temperature increase additionally brings about an increase in the amount of leakage.

Summary of the invention In contrast thereto, it is the object of the present invention to construct a fuel injection valve for the preliminary injection and the main injection wherein the preliminary injection charge is as constant as possible independently of the number of revolutions of the engine.

In accordance with the present invention, this object is attained by reason of the fact that the fuel being supplied constantly charges the preliminary injection piston and the loading piston and that the Working surface of the fuel at the valve needle when the injection valve being closed is greater than the working surface at the loading piston when the supply channel is closed. Moreover, there is also provided a stop for limiting the path of the preliminary injection piston and the fuel pressure can increase only after the preliminary injection piston rests against the stop and to such an extent that the loading piston opens the supply channel to the pressure chamber of the injection valve during the aforementioned increase of the closing spring tension while the working surface thereof for the fuel is increased and the loading piston moves up to the stop provided therefor.

In order to prevent fuel under pressure from flowing from the pressure chamber of the injection valve to the loading piston during the preliminary injection stage, a further embodiment of the present invention proposes that a check valve be disposed in the supply channel and arranged to block the direction of the flow of fuel from the pressure chamber to the loading piston.

Moreover, it is also contemplated that the channel between the preliminary injection piston and the pressure chamber of the injection valve should advantageously be relieved :after each main injection and for this reason it is proposed, in accordance with a further embodiment of the present invention, that the chambers which are separated by the preliminary injection piston are connected with each other by a channel which is blocked in the direction of the pressure chamber by means of a check valve. This particular channel which is provided with the check valve is preferably arranged within the preliminary injection piston.

In order to assure, on the one hand, an interval between the preliminary fuel injection stage and the main fuel injection stage and, on the other hand, a high opening pressure for the loading piston which gradually drops after opening of the injection needle, it is further proposed, according to yet another embodiment of the present invention, that the surface of the loading piston which is acted upon by the fuel pressure of the injection pump, while the injection valve and the supply channel are closed, be not greater than three-quarter the size of the surface which is decisive for producing the opening force at the injection needle.

BRIEF DESCRIPTION OF THE DRAWING The figure depicts a longitudinal cross-section through the fuel injection valve forming this invention with some elements thereof being shown in elevation.

DECRIPTION OF THE PREFERRED EMBODIMENT A nozzle holder 1 of the fuel injection valve is connected at one end by means of a perforated abutting fuel transfer member 2, on the one hand, with a pressure line (not shown) which extends from the injection pump and with a return passage which leads back to the fuel tank. On the other hand, and at the opposite end thereof and clamped to the nozzle holder 1 by means of a cap screw 4 is a nozzle body 3. An intermediate perforated body member 5 is disposed between the nozzle holder 1 and the nozzle body 3. As will be explained more fully hereinafter the nozzle holder 1 and the nozzle body 3 also include a preliminary injection piston 6, an axially disposed loading piston 7 and a valve needle 8 which together serve to control the flow of fuel.

A fuel inlet or supply channel 9 is provided in the abutting fuel transfer member 2 and is arranged to communicate with a branch line 10 which, in turn, feeds into a channel 11 provided within the nozzle holder 1. The preliminary injection piston 6 is slidably positioned in an enlarged bore 11a in the nozzle holder 1 at the opposite end of channel 11. The preliminary injection control means or piston 6 is urged into the bore by means of a spring 12, with its reciprocation in the bore being controlled by means of an abutment sleeve 13 which is confined in the chamber, as shown. A check valve 15, positioned in a suitable pocket provided in the preliminary injection piston 6, is arranged to control or block the flow of fuel from channel 11 into conduit 14 which is formed in the preliminary injection piston 6.

By means of communicating passages 16 which extend through the intermediate perforated body member 3 and the nozzle body 3 channel 11 is flow-connected with a pressure chamber pocket 17, the area of which is limited by the surrounding nozzle body 3 and the valve needle 8 which extends through the pocket. The diameter of the needle shaft 18 is greater than the diameter of the needle seat 19. Thus, it is believed it will be apparent that the fuel acts in the opening direction of the valve needle upon the differential annular surface which is thus produced. Moreover, another fuel supply channel 20 provided in nozzle holder 1 and nozzle body 3 terminates in the pressure chamber 17 and a check valve 21 which is provided in the perforated body member that is interposed between the nozzle holder 1 and nozzle body 3 allows the passage of the fuel only in the direction toward the pressure chamber 17. A flow connection between the fuel supply channel 9 and the interconnected channel 20 is controlled by means of the loading piston 7, and the latter comprises for this purpose a conical valve surface 7 which lifts off a valve seat 22 after a predetermined fuel pressure has been attained. The loading piston 7 is guided in a seal-type bushing 23 which is positioned in an axial bore provided in the nozzle holder. As explained before in connection with the needle shaft 18, the diameter of which is greater than the diameter of the needle seat 19, the diameter of the valve seat 22 is considerably smaller than the diameter of the conical nose 7 provided at the end of the loading piston 7.

The loading piston 7 and the valve needle 8 are acted upon by a common axially arranged spring 24 which determines the opening pressure at the valve seats 19 and 22. The spacedly arranged reduced opposed end portions of piston 7 and needle shaft 18 are each provided with annularly flanged bearing cap means 25 and Z6,

' respectively, which are adapted to receive the pressure of spring 24, as illustrated. Any fuel which happens to leak around the loading piston 7 as well as at the valve needle 8 into the spring chamber 27 is bypassed to the fuel tank by way of a leakage conduit 28 provided for this purpose.

For the proper operation of the fuel injection valve it is advantageous that, on the one hand, in the closed position of the valve of the loading piston and in the closed position of the valve needle, the surface area on loading piston 7 on which area the fuel impinges and which acts in the opening direction, is not more than three-quarters the size of the differential annular surface produced by the diameter of the needle shaft 18 and the diameter of the needle seat 19 which acts also in opening direction of valve needle 8. On the other hand, however, in the open position of the valve of the loading piston and in the open position of the valve needle, the surface area on piston 7 which area acts in the opening direction and the diameter of which is that of piston 7, is larger than the corresponding surface area on the valve needle 8, the diameter of this area *being that of needle section 18.

In view of the foregoing it is believed that it will be apparent that when the fuel flows under pressure from the injection pump through the pressure line (not shown) to the injection valve, the preliminary injection piston 6 will be initially displaced against the force of the spring 12 toward the abutment sleeve 13 due to the difference of the effective surfaces while the valve of the loading piston 7 and the valve needle 8 are closed, and the fuel which is displaced by the preliminary injection piston 6 will then cause the valve needle 8 to be lifted from the valve seat 19 against the force of the spring 24, thus permitting injection into the combustion chamber. The upward movement of valve needle .8 causes an increase of the force of spring 24 thus the closing force at the valve seat 22 is increased as well. After the unseating of valve needle 8 the fuel pressure gradually drops in response to the ejected fuel and to the gradually increasing needle surface exposed to pressure and acting in the opening direction. This decrease of pressure continues to a minimum value at which the valve needle will again close.

The check valve 21 prevents, during the preliminary injection operation, the flow of pressurized fuel from being transmitted from the pressure chamber 17 to the loading piston 7.

As soon as a specific pressure, which is greater than the pressure leading to the preliminary injection has again been built up in the fuel supply channel 9 and after the completion of the way of preliminary injection piston 6, the loading piston 7 is displaced from the valve seat 22 against the force of the spring 24 and against a stop 1a provided in the nozzle holder 1. The fuel will then flow through the channel 20 and past the check valve 21 into the pressure chamber 17. Thereafter, the valve needle 8 is again lifted olf the valve seat 19 against the force of the spring 24 and the main injection begins. Due to the pretensioning of the spring 24 caused by the stroke of the loading piston 7, the main injection pressure is greater than the preliminary injection pressure. When the injection pressure drops at the end of the feeding operation of the injection pump, the valve needle 8 will close first, since the charged surface thereof is smaller than that of the loading piston, and the loading piston 7 will close next. Excess pressures which arise in the pressure chamber 17 due to the closing movements of the valve needle 8 are eliminated by way of the check valve 15.

For the duration of the main fuel injection, the preliminary injection piston 6 is pushed into the starting position thereof by means of the spring 12.

Although several embodiments of the invention have been depicted and described, it will be apparent that these embodiments are illustrative in nature and that a number of modifications in the apparatus and variations in its end use may be effected without departing from the spirit or scope of the invention as defined in the appended claims.

What is claimed is:

1. In a fuel injection nozzle for preliminary and subsequent main injection having a bored body, a fuel supply inlet and a discharge outlet and a fuel chamber communicating with said discharge outlet, a fluid pressure operated valve needle movable in response to fluid pressure in said fuel chamber for opening and closing said discharge outlet, 2. loading piston for opening and closing said fuel supply inlet, a spring interposed between the loading piston and the valve needle, wherein the improvement comprises a fuel control piston means slidably mounted in said body and cooperable therewith to form a preliminary charge chamber, resilient means operably disposed between said fuel control piston means and said valve needle for biasing said control means in a direction away from said valve needle, plural fuel passage means in said body, at least a pair of which have the outlets thereof communicating with said fuel chamber, one of said fuel passage means forming a preliminary charge conduit means including said fuel control means having the inlet thereof cormnunicating with said fuel supply inlet and another fuel passage being in communication with said loading piston whereby said fuel control piston means and said loading piston are exposed to the fuel pressure prevailing in said fuel supply inlet so that the loading piston will subsequently move, due to the fuel pressure, down to a stop and thereby increases the tension of the closing spring until, after a further pressure increase of the fuel being supplied, the valve needle for the main injection charge opens.

2. In a fuel injection nozzle as claimed in claim 1, wherein at least a portion of said bored body is provided with a sleeve-type bushing including a valve seat and a radially extending fuel feed channel for one of said fuel passage means with the loading piston being positioned in said bushing, said piston in closed position further including surface means extending through said valve seat and exposed to the pressure of fuel supply, said surface having an area of not more than threequarters of the area of the valve needle exposed to the fluid pressure.

3. In a fuel injection nozzle as claimed in claim 1, wherein the preliminary charge chamber is provided with an abutment sleeve. forming a stop for the control piston means.

4. In a fuel injection nozzle as claimed in claim 1, wherein the fuel supply inlet and the fuel chamber communicating with the discharge outlet are connected by a bypass which is blocked in the direction of the fuel chamber by means of a check valve, preferably arranged within the control piston.

5. In a fuel injection nozzle as claimed in claim 1, wherein the plural fuel passage means extend through three longitudinally aligned elements comprising said body.

6. In a fuel injection nozzle as claimed in claim 5, wherein the intermediate element includes a check valve.

References Cited UNITED STATES PATENTS 9/1939 Bischof 239533 X 9/1960 Engel 239 

